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14

It's a rather late answer, but the paper Visible optical beats at the hertz level has just appeared on the Arxiv and this describes exactly the phenomenon you ask about. This image from the paper shows the experimental setup: The light frequency is modified using acousto-optic modulators (labelled AOM in the diagram), and to make it look pretty a lens is ...


7

Sound waves do generate changes in temperature because the propagation of sound is an approximately isentropic process. Keep in mind though that changes in static temperature can very well occur without the generation of heat. Moreover, the pressure changes associated with sound waves are of such a small magnitude that the observable temperature changes are ...


6

Sound is attenuated in air - this is an irreversible, lossy process that results in the heating of the air. You can conclude that it is not an isentropic process. See my recent answer to another question for some of the math behind this - showing that while the amount of heating is very small, it is not zero. For practical purposes (for example, for ...


5

Put more simply: sound waves are attenuated as they propagate through air (this is more easily measured for very short wavelengths, e.g. ultrasound). This means they lose energy - which is turned into heat of the air. The amount of heating, however, is very very small. Let's do the math. A sound wave of 120 dB (really loud) has energy of only $1 ...


3

Heat corresponds to random movements of atoms and molecules. It travels only through conduction - slowly. Sound consists of ordered movements, travelling through a medium as a wave (although it can also stand still, as in a standing wave). Large numbers of atoms or molecules move back and forth in synchrony. Sound eventually becomes random, as it is ...


3

I'm not an expert, but it seems to me that the it is mono-sound. Stereo means sound coming from two independent sound channels. As there is only one source, and both sounds are the same, I would consider it mono-sound. See Wiki Stereo


3

Isentropic processes are ones with constant entropy. Since entropy is defined as dS = dQ/T, then a reversible adiabatic process with dQ = 0 is an isentropic process. Need to take a step back to understand this. First, the physics of waves in gases come from the fluid equations. These include conservation of mass, momentum and energy. These three ...


3

A plank is a complicated example to choose because it's a composite material with a complicated structure. A better choice would be a piece of iron or some other homogeneous material. In that case the speed of sound is given by: $$ v = \sqrt{\frac{K + \tfrac{4}{3}G}{\rho}} $$ where $K$ is the bulk modulus and $G$ is the shear modulus. The bulk modulus is ...


2

I guess you mean to ask - is the amplitude of the vibration proportional to the speed of the sound waves it produces? The speed of sound in an ideal gas for relatively small amplitudes ($\frac{\Delta P}{P} \ll 1$) is $v=\sqrt{\frac{\gamma P}{\rho}}$ where $\gamma$ is the adiabatic constant (i.e. $PV^\gamma=const$), P is the average pressure, and $\rho$ is ...


1

The statement in the first paragraph "In fact, today’s standard turbines are based on the same physical principles as 18th century windmills." is marketing hooey. They are hanging their hat on the fact that the windmills were unducted props and most of today's turbines are the same, which is true. The airfoils used today are not 18th century designs. They ...


1

There's an error in that the type of pipe for each of the two fundamental frequencies as described in your comment don't match the problem description. The pipe with a fundamental frequency of 440Hz is open-closed, and the pipe with a fundamental frequency of 660Hz is open-open. You actually said "closed-closed", which isn't even an option, but even if ...


1

Sometimes I just have to say LM--Y: http://www.amazon.com/Prestige-Medical-131-BLK-Stereo-Stethoscope/dp/B001ULDA9Q The word "stethoscope" is a generic term for any tool that enhances detection of subcutaneous sounds. You can use a stick or metal rod, or you can use digital transducers with Bluetooth. Now, in a more general answer: you are correct that ...


1

No voice sings in a "pure tone", i.e., while the voice is in tune, the sound signal is composed of various harmonic frequencies. This gives you the "color" of the voice, and that makes the two voices distinct.


1

The answer to your question is yes, we can observe beat notes between two different coherent sources of light. This fact underlies almost every precision laser experiment because it allows for lock-in detection. However, there is a subtle difference from audio beatnotes. The difference is that with sound the oscillations are in the air pressure which is ...


1

Due to evaporation a layer of air forms between the water droplet and the hot surface which causes the system to vibrate by letting air escape in bursts and produce sound. I suggest reading about the description of the sound that was recorded in the Leidenfrost experiment. Article: http://www.nature.com/srep/2012/121010/srep00720/full/srep00720.html Video: ...


1

If you have a small diapragm moving slowly then the air will just flow around it and you won't get any appreciable pressure rise in front of the diaphragm. That means there won't be any longitudinal pressure waves (i.e. sound waves) generated normal to the diaphragm surface. If you now make the diaphragm larger the air has farther to move to get to the ...


1

To expand on Xcheckr's answer: The full equation for a single-frequency traveling wave is $$f(x,t) = A \sin(2\pi ft - \frac{2\pi}{\lambda}x).$$ where $f$ is the frequency, $t$ is time, $\lambda$ is the wavelength, and $x$ is position. This is often written as $$f(x,t) = A \sin(\omega t - kx)$$ with $\omega = 2\pi f$ and $k = \frac{2\pi}{\lambda}$. If you ...


1

I can't tell what exactly you may have heard, but sounds reflect off of all kinds of things, particularly flat walls, so echos from a loud sound like thunder is quite plausible. 5 seconds is about 1 mile of total propagation, so that again is plausible. Lightning is a large current that ionizes the air in its immediate vicinity. Such ionized air is ...


1

There's not much difference. Thermal vibrations would be perceived as sound (noise) if they were intense enough, but they are not. The thermal vibration amplitudes at room temperature are small enough that the ear is not sensitive to them. I've been told that the sound pressure level for thermal vibrations is close to, but below, the threshold of ...


1

If a system returns to the initial conditions after a process, then that process has been reversed and (assuming one of the initial conditions is the temperature) is isentropic. Once a sound ends, the molecules remain in essentially the same position as before the sound. Drastic increases or decreases in the number of molecules at the source (explosions) ...


1

A qualitative picture of what happens in a gas can be made in terms of whether the behavior is random or non-random, oscillatory or steady. Temperature describes the random motions of the particles that comprise some object. Correlations, if they exist, disappear rapidly with distance between particles. In an ideal gas, correlations don't exist, period. ...



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